Composite charts
Two ways of making one chart out of two birth charts: the composite, built from the midpoint of each pair of planets, and the Davison chart, the real sky at the moment and the place halfway between the two births.
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Two ways to make one chart
The composite chart grew out of the midpoint work of German astrologers in the 1920s, was set out in English in John Townley’s book The Composite Chart in 1973, and was made widely known by Robert Hand’s Planets in Composite in 1975. It is not a sky that ever existed: each of its planets is the degree halfway between the two people’s placements of that planet. The Davison chart, from Ronald Davison’s book Synastry in 1977, takes the other road and casts an ordinary chart for a real moment and place, the ones halfway between the two births, so its planets are where they actually stood then.
How they are worked out here
For the composite, each body’s position is the nearer midpoint of the two, halfway the short way round. When both birth times are known the midheaven is the midpoint of the two midheavens and the ascendant the midpoint of the two ascendants. Some astrologers work the ascendant out from the composite midheaven and the latitude where the couple live instead, which can give a different sign, so this wheel draws no houses. Its aspects are measured with the same orbs as every chart on this site. For the Davison chart the two birth moments are turned into universal time and averaged, and so are the birthplaces: the latitudes directly, the longitudes the shorter way round the globe. The chart for that minute and place comes from the same astronomy as your own. Both need the two birth times for an ascendant; without one, the Moon may also be several degrees out.
A worked example
Take one Sun at 10° Aries and the other at 20° Gemini. Counted from the start of Aries those are 10° and 80° of the circle, the average is 45°, and the composite Sun stands at 15° Taurus. Now move the second Sun to 20° Libra, which is 200°. A plain average gives 105°, or 15° Cancer, but that point lies on the long side of the circle, 95° from each Sun. The two are only 170° apart going the other way, so the nearer midpoint is the one opposite, 15° Capricorn, and that is the one a composite uses. Each pair is settled on its own like this, which is why a composite can show things no sky does: Mercury is never more than 28° from the Sun in a birth chart, yet a composite Mercury can land opposite the composite Sun.
The Davison chart averages dates instead of degrees. For two people born at noon on 10 June 1988 and on 20 June 1990 the births are 740 days apart, so the chart is cast for noon on 15 June 1989, 370 days after the first. The place is found the same way. For someone born in London and someone born in New York it falls in the middle of the North Atlantic; for Chicago and Miami, in Georgia, not far from Atlanta. It does not matter that neither of them has been there: the place only fixes the horizon of the chart.
What they claim
Both charts are read as a picture of the relationship itself rather than of either person, and the tradition looks at them much as it looks at a birth chart: where the Sun and Moon fall, and what the planets do to each other. A composite is a set of averages and a Davison chart is a moment between two births. Neither describes a future, and this page predicts nothing about the two people.
How astrologers read one
The usual order is the one used for a birth chart. The composite Sun is taken as what the pair is about, the Moon as how it feels from inside, and Venus and Mars as the way affection and friction show. After that come the tightest aspects. The Davison chart has one thing the composite lacks, a date of its own, so some astrologers progress it or watch transits to it as they would for a person. Friends, relatives and business partners are read with the same two charts; nothing in the arithmetic is about romance.
To compare the two whole charts without merging them, use Compatibility, which reads a pair on five axes. The same halfway arithmetic inside a single chart is on Midpoints, what each aspect is taken to mean is under The aspects, and your own chart is on the front page.
Questions people ask
What is a composite chart?
A composite chart combines two birth charts into one by taking the midpoint of each pair of placements: halfway between the two Suns, halfway between the two Moons, and so on for every planet, always the shorter way round the zodiac. The result is a set of averages rather than a sky that ever existed, and astrology reads it as a portrait of the bond between two people rather than of either one alone. This page draws it as a wheel and lists the aspects between its midpoints.
What is a Davison chart?
A Davison chart is an ordinary chart cast for a real moment and place: the instant exactly halfway between two births, seen from the point halfway between the two birthplaces. Because it is a real sky, its planets stand where they actually stood, retrograde ones included, and with both birth times it has an ascendant and houses like any birth chart. That is what sets it apart from a composite. This page converts both births to universal time and takes the average, then averages the two latitudes and longitudes as well.
What is the difference between a composite chart and synastry?
Synastry lays two birth charts side by side and compares them, looking at how one person’s planets fall against the other’s, so both charts stay whole. A composite or Davison chart does the opposite and merges the two into a single chart, which astrology reads as the relationship taken as something of its own. Many astrologers use both: synastry for how two people meet each other, a composite for what they make together. The compatibility page on Solstaria does the first, and this page the second.
Do I need both birth times for a composite chart?
Only for the angles and houses. Without both times there is no composite ascendant or midheaven, and the Davison chart has no ascendant or houses. A missing time is counted from midday, and because the Moon moves about half a degree an hour its position can then be several degrees out. Neither set of details leaves the browser: your own are saved on this device as your profile, and the other person’s under a separate entry that the Forget their details button clears.
Composite or Davison: which one should I use?
Astrologers are split, and many look at both. The composite reached print first and is the more widely used of the two, and most books on relationship charts, starting with Robert Hand’s, describe it. Its weakness is that it is a set of averages with no date, so its planets can stand in ways no real sky allows. The Davison chart is a real moment with real planets, which lets it be handled like any birth chart, but its place is often a spot neither person knows. For people close in age the two tend to agree on the slowest planets and differ most on the Moon and the angles.